In a system that supplies anode gas (hydrogen gas) to a fuel cell, an anode circulation system that supplies anode off-gas discharged from the anode of the fuel cell back to the anode has hitherto been used. In such a system, Japanese Patent Laid-Open No. 2003-317766 discloses a technique for eliminating clogged drain by opening a purge valve when the clogged drain occurs within a fuel cell.